Intervertebral linking device

ABSTRACT

One embodiment includes at least a fixed element designed to be secured to a vertebra or sacrum, at least a mobile linking element and at least an intermediate element that articulates the mobile element relative to the fixed element. The intermediate element is received in an internal volume of the mobile element and is deformable, so as to be introduced by impingement into the inner volume. The fixed element is received at least partly in an internal volume of the intermediate element and has a position for use wherein said fixed element has three degrees of freedom in rotation, but is linked in translation, relative to the intermediate element.

[0001] The present invention relates to an intervertebral linkingdevice.

[0002] Such a device is known which comprises at least two pedicularscrews, each of which has a first end secured to a correspondingvertebral body, a bulging intermediate portion, and a second, threaded,end. Auxiliary members, provided with an arch for fastening a rodextending between the vertebrae, are located on each of theabove-mentioned bulging portions. A bolt co-operating with the threadedend of each screw enables each auxiliary member to be immobilised, oncethat member has been put in place, in an appropriate manner.

[0003] However, this known device has some disadvantages in that itinvolves a relatively delicate mounting process. In addition, onceimplanted, it does not offer any degree of freedom between the variouselements constituting it. Thus, when forces are exerted in the region ofthe vertebral bodies, the absence of a degree of freedom brings about atransmission of these forces onto the whole of the device, so that thedevice has a tendency to become separated from the vertebrae which itconnects, and also brings about dysfunctions in the entire vertebralchain.

[0004] In order to overcome those various disadvantages, the presentinvention proposes to provide a device whose structure is simple, whosemounting is easy and which is reliably implanted in the vertebrae whichit connects.

[0005] To that end, the invention relates to an intervertebral linkingdevice which is to connect at least two vertebrae to one another,characterised in that it comprises:

[0006] at least one fixed element which is to be secured to a vertebraor to the sacrum,

[0007] at least one mobile linking element suitable for being displacedrelative to the or each fixed element,

[0008] and also at least one intermediate element permitting thearticulation of the or each mobile element relative to the or each fixedelement,

[0009] in that the or each intermediate element is received, in use, inan internal volume of the mobile element, or of the fixed element, theintermediate element being deformable so that it can be introduced byimpaction into that internal volume,

[0010] and in that the fixed element, or the mobile element, is receivedat least partially, in use, in an internal volume of the intermediateelement, the fixed element or the mobile element having, with theintermediate element, a mutual position of use in which the fixedelement or the mobile element has three degrees of freedom in rotation,but is linked in translation, relative to the intermediate element, anda mutual position of introduction in which the fixed element, or themobile element, has three degrees of freedom in rotation and intranslation relative to the intermediate elements.

[0011] According to other features of the invention:

[0012] the intermediate element assumes the form of a cup;

[0013] the internal volume of the intermediate cup is bordered by atruncated spherical surface;

[0014] the intermediate cup has a truncated spherical external surfacewhich is concentric with the internal surface;

[0015] the internal and external surfaces define a wall of theintermediate cup;

[0016] the thickness of the wall is from 0.5 to 3 mm, preferably from 1to 1.5 mm;

[0017] the intermediate element is produced from polyethylene.

[0018] The invention will be described hereinafter with reference to theappended drawings which are given purely by way of non-limiting exampleand in which:

[0019]FIG. 1 is a view in longitudinal section illustrating the variouselements constituting an intervertebral linking device according to theinvention;

[0020]FIGS. 2A, 2B and 2C are views analogous to FIG. 1 illustrating twosteps in the mounting of an intermediate element of the device of FIG. 1in the internal volume of a mobile element of that device; and

[0021]FIGS. 3A and 3B are views analogous to FIG. 1 illustrating theintroduction of a fixed element of the device of FIG. 1 into theinternal volume of the intermediate element.

[0022] The linking device illustrated in FIG. 1 comprises a pedicularscrew 2 which is to be secured in a vertebral body (not shown).

[0023] This pedicular screw, which constitutes a fixed element of thelinking device, is provided with a rod 3 terminated by a spherical head4 which comprises an equatorial flat portion 6. The latter extends in aninclined manner to the effect that it is not perpendicular to theprincipal axis A of the screw 2.

[0024] The head 4 is also hollowed out, on the opposite side to the rod3, with a blind hole 8. The latter is to receive a control device (notshown) which is, for example, the end of a screwdriver or of a hexagonalkey.

[0025] The linking device of FIG. 1 also comprises a mobile elementwhich is illustrated partially and which is generally indicated by thereference 10. This element has a body 12 which extends between the twovertebrae that are to be connected by the device of the invention. Thisbody is terminated by two hollow ends, only one of which, 14, is shown.

[0026] Each end defines a housing 16 which constitutes an internalvolume of the element 10 and which is bordered by walls 18 forming aportion of a sphere. The transverse dimension 1 of the opening 16′ ofthe housing 16 is smaller than the diameter L of the housing.

[0027] Finally, the device of FIG. 1 comprises an intermediate element20 which constitutes a cup. The cup, which has a truncated hemisphericalshape, has a thin wall 22 which extends from a base 24 of the cup.

[0028] The external surface 26 of the wall 22 delimits a portion of asphere, the diameter of which is identical to that L of the housing 16.In addition, the internal surface 28 of the wall 22, which forms aninternal volume 30 of the cup 20, has a diameter D identical to that ofthe head 4.

[0029] Furthermore, the transverse dimension d of the opening 32 of theinternal volume 30 is equal to that of the flat portion 6 of the head 4.The opening is more “narrow” than the internal volume inasmuch as thespherical internal surface 28 extends at an angle of more than 180°.

[0030] Finally, the base 24 of the cup 20 is hollowed out with anorifice 34 permitting the passage of a control tool in the directiontowards the blind hole 8 of the pedicular screw 2.

[0031] It should be noted that the cup 20 is produced from a deformablematerial, such as polyethylene. This feature, in association with thethinness of the wall 22, enables the cup 20 to be introduced byimpaction into the housing 16 of the mobile element 10. The thickness eof the wall 22 is, for example, from 0.5 to 3 mm, preferably from 1 to1.5 mm.

[0032] The mounting of the linking device illustrated in FIG. 1 will nowbe described with reference to FIGS. 2A, 2B, 2C, 3A and 3B.

[0033] First of all, the cup 20 has to be introduced into the internalvolume 16 of the mobile element 10.

[0034] For that purpose, as shown in FIG. 2A, the cup 20 is disposed insuch a manner that it is facing the housing 16. Subsequently, it isbrought axially closer to the mobile element 10, in accordance with thearrow F.

[0035] Given that the cup 20 is resiliently deformable, its transversedimensions, in particular the inside diameter D of its wall 22, arecapable of undergoing a momentary reduction. This therefore enables thecup 20 to be introduced by impaction in accordance with the arrow F intothe housing 16 of the mobile element 10 (FIG. 2B).

[0036] Once that operation has been carried out, as shown in FIG. 2C,the external surface 26 of the thin wall 22 extends in contact with theinternal surface 18 of the housing 16, having the same diameter. Thus,the cup 20 has three degrees of freedom in rotation relative to themobile element.

[0037] On the other hand it has no degree of freedom in translationrelative to the element 10 in this position of use, since the peripheryof the opening 16′, the transverse dimension of which is smaller thanthe diameter of the housing 16, prevents the cup 20 from coming out ofthe housing again.

[0038] It is then necessary to introduce the spherical head 4 of thescrew 2 into the housing 30 of the cup 20.

[0039] For that purpose, the screw 2 is first of all inclined in such amanner that the flat portion 6 extends horizontally in FIG. 3A, that isto say, perpendicularly to the principal axis of the cup 20. The cup 20is then brought closer to the screw 2 in accordance with a translationparallel with the principal axis of the cup 20 (arrow F′).

[0040] Given that the transverse dimension of the flat portion is equalto that d of the opening 32 of the housing 30, this enables the head 4to be freely introduced into the housing.

[0041] Subsequently, the head 4 is pivoted inside the housing in such amanner that the flat portion 6 is no longer facing the above-mentionedopening 32. In this position of use (FIG. 3B), the head 4 is free topivot relative to the housing 30 but has no degree of freedom intranslation relative to the cup 20.

[0042] The diameter D of the head 4 is larger than the transversedimension of the opening 32. In addition, the periphery of the opening32 is rendered substantially rigid owing to the presence of the rigidwalls of the mobile element 10. Thus it is almost impossible for theperiphery of the opening 32 to be deformed radially, which prevents thehead 4 from coming out of the internal volume 30 again.

[0043] Once the device has been placed in the configuration of FIG. 3B,it is necessary to fix the pedicular screw 2 in a correspondingvertebral body by means of a control device co-operating with the blindhole 8.

[0044] By way of a variation in mounting, it is possible first of all tofix each pedicular screw in a corresponding vertebral body. Then eachcup 20 is introduced into a corresponding internal volume 16 of themobile element, as explained in FIGS. 2A to 2C.

[0045] The fixed element and the mobile element are then brought closerto one another and the cup 20 is caused to tilt within its housing 16.This tilting may be effected by means of a rod (not shown) forming aprobe which comes into contact with the base 24 of the cup 20 from theorifice or the housing 16 opposite the pedicular screw 2.

[0046] Finally, the intermediate element 20 so tilted is brought closer,relative to each screw 2, so that each flat portion 6 can permit theintroduction of a corresponding screw into the internal volume 30.

[0047] Once the device of the invention has been placed in theconfiguration of FIG. 3B, it is possible to fit onto the flat portion 6an advantageously removable stop means, such as a screw 36. The latter,by limiting the pivoting of the head 4 relative to the cup 20, preventsthe head from recovering its position in FIG. 3, which avoids anyinadvertent separation between the cup 20 and the screw 2.

[0048] The invention is not limited to the example described andrepresented.

[0049] Thus, the intermediate cup 20 may be received in a housing withwhich the pedicular screw, and not the mobile element, is equipped.Under those conditions, the mobile element then has a spherical head,similar to the head 4, suitable for being introduced into the internalvolume of the intermediate cup.

[0050] Furthermore, the screw 2, the mobile element 10 and theintermediate cup 20 are capable of having other arrangements, such asthose described in French Patent Application 00 08522, filed on 30 Jun.2000 by the present Applicant, and also those described in InternationalPatent Application PCT-FR-01/02098, filed on 29 Jun. 2001 by the presentApplicant.

[0051] The invention enables the objectives mentioned above to beachieved.

[0052] The various elements constituting the intervertebral linkingdevice of the invention have a relatively simple structure.

[0053] The assembly of these elements is particularly easy for thesurgeon because the intermediate element can be introduced by impactioninto the internal volume of the mobile element, or of the fixed element.

[0054] Then, the presence of the intermediate element permits the mutualmounting of the fixed and mobile elements, even if there is practicallyno clearance in rotation between those two elements.

[0055] Moreover, it should be noted that, even though the intermediateelement is deformable, which facilitates the mounting thereof, itbecomes substantially rigid once introduced into its housing. Thisrigidity, which is conferred on it by the rigid walls of the housing,provides satisfactory stability for the device, once implanted.

[0056] Thus the device has a high degree of resistance in respect ofmechanical stresses exerted, in particular, in traction. In addition,the presence of the intermediate element allows any forces to which thelinking device of the invention is subjected to be transmitted only to avery slight extent.

1. Intervertebral linking device to connect at least two bones of thespine to one another, comprising: at least one fixed which is to besecured to a vertebra of the spine or to a sacrum of the spine, at leastone mobile linking element suitable for being displaced relative to eachfixed element, at least one intermediate element permitting thearticulation of each mobile linking element relative to the at least onefixed element, wherein each intermediate element is received, in aninternal volume of a corresponding one of the at least one mobilelinking element, or of a corresponding one of the at least one fixedelement, the intermediate element being deformable to be placed into theinternal volume by impaction, and wherein the at least one fixedelement, or the at least one mobile linking element, is received atleast partially in an internal volume of the intermediate element havinga mutual position of use with three degrees of freedom in rotationrelative to the intermediate element while remaining linked intranslation and a mutual position of introduction in which thecorresponding one of the at least one fixed element, or thecorresponding one of the at least one mobile element, has three degreesof freedom in rotation and in translation relative to the intermediateelement.
 2. Linking device according to claim 1, wherein theintermediate element assumes the form of a cup.
 3. Linking deviceaccording to claim 2, wherein the internal volume of the intermediatecup is bordered by a truncated spherical surface.
 4. Linking deviceaccording to claim 3, wherein the intermediate cup has a truncatedspherical external surface, which is concentric with the internalsurface.
 5. Linking device according to claim 4, wherein the internalsurface and the external surface define a wall of the intermediate cup.6. Linking device according to claim 5, wherein the thickness of thewall is from 1 to 1.5 mm.
 7. Linking device according to claim 1,wherein the intermediate element is produced from polyethylene.